Dynamic thermal management spray system

ABSTRACT

A dynamic thermal management spray system for efficiently thermally managing one or more electronic devices. The dynamic thermal management spray system includes one or more spray units having an adjustable spray characteristic. The spray characteristic of at least one spray unit is adjusted based upon the desired thermal management of one or more electronic devices. Adjusting the spray characteristic is preferably comprised of increasing/decreasing the fluid flow rate.

CROSS REFERENCE TO RELATED APPLICATIONS

I hereby claim benefit under Title 35, United States Code, Section 120of U.S. patent application Ser. No. 10/243,683 filed Sep. 13, 2002 whichis subject to a restriction requirement. This application is adivisional of the Ser. No. 10/243,683 application. The Ser. No.10/243,683 application is now U.S. Pat. No. 6,857,283. The Ser. No.10/243,683 application is hereby incorporated by reference into thisapplication. Two additional divisional applications from theabove-stated application have been filed relating to this applicationidentified by U.S. Ser. No. 10/723,608 and Ser. No. 10/723,607.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable to this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to electronic device burn-insystems and more specifically it relates to a dynamic thermal managementspray system for efficiently thermally managing one or more electronicdevices.

2. Description of the Related Art

Thermal management systems for electronic device burn-in equipment havebeen in use for years. Conventional thermal management systems utilizedtoday are comprised of, for example, either air-cooled enclosures, orfluid-cooled cold plates. Upcoming technologies include refrigerationsystems or other two-phase based technologies.

When producing electronic devices, manufacturers typically perform threedifferent tests on the electronic devices prior to shipping: (1) sort,(2) burn-in, and (3) class testing. Sort test requires maintaining thewafers at a modest temperature, e.g. 35° Celsius, while the wafers areprobed for defects. Conventional fluid-cooled cold plates are employedat this stage. Projected heat fluxes, even at the wafer sort, arepointing to the fact that a more effective thermal management technologyis needed at this stage.

Burn-in of the electronic devices is typically accomplished utilizingelevated voltages and temperatures in a process that raises the junctiontemperatures of a batch of electronic devices. The lifespan of anelectronic device is closely related to its operating temperaturewherein operating under increased temperatures reduces the effectivelifespan of the electronic device. By applying increased voltages andtemperatures to an electronic device, the weaker electronic devices willfail during testing. The length of the burn-in of electronic devices isdirectly tied to the median junction temperature of the batch ofelectronic devices. It is therefore important to maintain a relativelynarrow junction temperature spread that provides a higher mediantemperature. For example, a poor thermal management system can produce ajunction temperature spread from 75° to 125° Celsius resulting in a lowmedian junction temperature, longer burn-in time and higher associatedburn-in costs. Modern fluid-based thermal management systems arecurrently able to lower the junction temperature spread to approximately95° to 110° Celsius thereby reducing burn-in time and burn-in costs.

Class test is the final step in the testing process and is comprised ofa final series of tests to validate functionality and quantify speeds.During class test, non-uniform heating of the electronic devicestypically occurs. A electronic device's speed is typically derated by0.15% for every degree Celsius rise above the target temperature(junction temperature, Tj). It is therefore important to maintain thetemperature of the electronic devices relatively close to the targettemperature (Tj).

Due to increasing chip heat fluxes (projected to exceed 125 W/cm² by theyear 2004), conventional thermal management systems for electronicdevice burn-in are reaching their cooling limits. A further problem withconventional thermal management systems is that they are inefficient,complex, costly to implement and costly to operate. A further problemwith conventional thermal management systems is that the resultingjunction temperature spreads result in relatively long burn-in times ofthe electronic device devices. Another problem with conventional thermalmanagement systems is that they require significant amounts of power tooperate.

While these devices may be suitable for the particular purpose to whichthey address, they are not as suitable for efficiently thermallymanaging one or more electronic devices. Conventional dynamic thermalmanagement spray systems are inaccurate and inefficient therebyincreasing the testing costs for an electronic device manufacturer.

In these respects, the dynamic thermal management spray system accordingto the present invention substantially departs from the conventionalconcepts and designs of the prior art, and in so doing provides anapparatus primarily developed for the purpose of efficiently thermallymanaging one or more electronic devices.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing disadvantages inherent in the known types ofelectronic device burn-in systems now present in the prior art, thepresent invention provides a new dynamic thermal management spray systemconstruction wherein the same can be utilized for efficiently thermallymanaging one or more electronic devices.

The general purpose of the present invention, which will be describedsubsequently in greater detail, is to provide a new dynamic thermalmanagement spray system that has many of the advantages of theelectronic device burn-in systems mentioned heretofore and many novelfeatures that result in a new dynamic thermal management spray systemwhich is not anticipated, rendered obvious, suggested, or even impliedby any of the prior art electronic device burn-in systems, either aloneor in any combination thereof.

To attain this, the present invention generally comprises one or morespray units having an adjustable spray characteristic. The spraycharacteristic of at least one spray unit is adjusted based upon thedesired thermal management of one or more electronic devices. Adjustingthe spray characteristic is preferably comprised ofincreasing/decreasing the fluid flow rate.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofmay be better understood and in order that the present contribution tothe art may be better appreciated. There are additional features of theinvention that will be described hereinafter and that will form thesubject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of the description and should not beregarded as limiting.

A primary object of the present invention is to provide a dynamicthermal management spray system that will overcome the shortcomings ofthe prior art devices.

A second object is to provide a dynamic thermal management spray systemthat efficiently thermally manages one or more electronic devices.

Another object is to provide a dynamic thermal management spray systemthat thermally manages one or more electronic devices by adjusting thefluid flow rate sprayed upon the electronic devices.

Another object is to provide a dynamic thermal management spray systemthat minimizes junction temperature spread during electronic devicetesting procedures.

An additional object is to provide a dynamic thermal management spraysystem that is energy efficient, flexible and relatively small in size.

Another object is to provide a dynamic thermal management spray systemthat is capable of cooling a variety of electronic device devices usingthe same burn-in equipment.

An additional object is to provide a dynamic thermal management spraysystem that transfers heat from an electronic device using conduction,convection, phase change or a combination thereof.

Another object is to provide a dynamic thermal management spray systemthat works with existing and various types of burn-in and thermalmanagement equipment currently utilized in the industry.

Another object is to provide a dynamic thermal management spray systemthat is capable of managing the temperature of electronic devices thatutilize an integrated heat sink and electronic devices that do notutilize an integrated heat sink.

A further object is to provide a dynamic thermal management spray systemthat is capable of thermally managing one or more electronic devices ofvarious shapes, sizes and structures.

Other objects and advantages of the present invention will becomeobvious to the reader and it is intended that these objects andadvantages are within the scope of the present invention.

To the accomplishment of the above and related objects, this inventionmay be embodied in the form illustrated in the accompanying drawings,attention being called to the fact, however, that the drawings areillustrative only, and that changes may be made in the specificconstruction illustrated and described within the scope of the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will become fully appreciated as the same becomes betterunderstood when considered in conjunction with the accompanyingdrawings, in which like reference characters designate the same orsimilar parts throughout the several views, and wherein:

FIG. 1 is a schematic diagram illustrating the overall structure of thepresent invention.

FIG. 2 is a block diagram illustrating the communication connectionsbetween the control unit and the related components of the presentinvention.

FIG. 3 is a flowchart illustrating the overall operation of the presentinvention.

FIG. 4 is an upper perspective view of an exemplary spray enclosure witha burn-in board positioned within.

FIG. 5 is an upper perspective view of the exemplary spray enclosurewith the burn-in board removed illustrating the spray assembly withinthe spray enclosure.

FIG. 6 is a cross sectional view taken along line 6—6 of FIG. 5illustrating the spray assembly within the exemplary spray enclosure.

FIG. 7 is an upper perspective view of the upper portion of the sprayassembly.

FIG. 8 is an upper perspective view of the lower portion of the sprayassembly.

FIG. 9 is an upper perspective view of an exemplary burn-board.

FIG. 10 is an upper perspective view of a spray assembly.

FIG. 11 is an exploded upper perspective view of the spray assembly.

FIG. 12 is a top view of the spray assembly.

FIG. 13 is an upper perspective view of the spray assembly inverted withthe rear plate removed.

FIG. 14 is a bottom view of the spray assembly with the rear plateremoved.

FIG. 15 is a side view of the spray assembly illustrating the movementof the second portion within the first portion.

FIG. 16 is a side cutaway view of the spray assembly dispensing fluidupwardly upon the electronic device having a higher profile (e.g.containing an integrated heat sink) within a socket of the burn-inboard.

FIG. 17 is a side cutaway view of the spray assembly dispensing fluidupwardly upon the electronic device having a lower profile (e.g. nointegrated heat sink) within a socket of the burn-in board with thesecond portion fully extended from the first portion.

FIG. 18 is a side cutaway view of a dynamic spray control for the sprayunits.

DETAILED DESCRIPTION OF THE INVENTION

A. Overview

Turning now descriptively to the drawings, in which similar referencecharacters denote similar elements throughout the several views, FIGS. 1through 18 illustrate a dynamic thermal management spray system 10,which comprises a reservoir 80 for storing a volume of fluid, a mainpump 82 fluidly connected to the reservoir 80, and a plurality of sprayunits 40 fluidly connected to the main pump 82. The spray units 40dispense the fluid upon the surface of the electronic device 18 duringburn-in or thermal management thereby maintaining a relatively constanttemperature. In the present embodiment of the invention, each of thespray units 40 includes a stationary first portion 50 with a secondportion 54 movably positioned within the first portion 50 in a biasedmanner. When burning in electronic devices 18 without an integrated heatsink that are deeply recessed within the sockets 14 of a burn-in board12, the fluid pressure to the second portion 54 is preferably increasedthereby extending the second portion 54 from the first portion 50thereby reducing the effective distance from the surface of theelectronic device 18.

The invention described herein relates to a stand-alone burn-in system.In other words, the thermal management system, the burn-in boards andchips, and the control system are all packaged into a stand-alone pieceof equipment. However, it can be appreciated that the present inventionmay be embodied in an alternative form that can be described as having acentral pump/control station that services multiple satellite burn-instations serviced by a central reservoir 80, as well as a common fluiddistribution system. In addition, the present invention is suitable forother spray cooling applications such as thermal management of one ormore electronic devices.

B. Spray Enclosure

FIGS. 4 through 6 illustrate an exemplary spray enclosure 20 having aninterior cavity 22 for receiving at least one burn-in board 12. Thespray enclosure 20 may be comprised of any structure capable of housinga burn-in board which are commonly utilized within the burn-in industryor other unit not utilized within the burn-in industry. The sprayenclosure 20 preferably has an opening and a door for selectivelyclosing and sealing the opening as is conventional with spray enclosures20 utilized within the burn-in industry. The spray enclosure 20preferably has a rail structure 16 or other structure for receiving andsupporting one or more burn-in boards 12 in a desired position withrespect to the corresponding spray assembly 30. It can be appreciatedthat the spray units 30 and the burn-in boards 12 may be stacked withinthe interior cavity 22 of the spray enclosure 20 depending upon thetotal number of burn-in boards 12 to be utilized simultaneously. Thepresent invention may also be configured to receive a self-containedrack unit containing a plurality of arrays of spray assemblies 30 forallowing quick changing of the electronic devices thereby increasing theoperational time of the burn-in system.

It can be appreciated that the spray enclosure 20 may have variousstructures and configurations not illustrated within FIGS. 4 through 6of the drawings that may be suitable for usage with the presentinvention. U.S. Pat. No. 5,880,592 provides an exemplary burn-in sprayenclosure 20.

As shown in FIGS. 4 and 5 of the drawings, an inlet tube 24 extends intothe spray enclosure 20 for providing the fluid to the spray assembly 30as will be discussed in further detail. As further shown in FIGS. 4 and5 of the drawings, an outlet tube 26 extends from the spray enclosure 20returning the fluid recovered from the spray enclosure 20 to thereservoir 80.

U.S. Pat. No. 6,108,201 entitled Fluid Control Apparatus and Method forSpray Cooling to Tilton et al. also describes the usage of spraytechnology to cool a printed circuit board. Spray thermal management maybe performed locally (i.e. where the chip is sprayed directly), globally(i.e. where the chip and surrounding electronics/boards are alsosprayed), a combination of locally and globally, or in conjunction withair cooling or other cooling methods. In a spray thermal managementsystem, most if not all of the spray components are contained within thespray chassis such as but not limited to the spray unit, the card cage,valves, pumps, filters, separators and the like.

C. Burn-In Board

The present invention may utilize various structures and types ofburn-in boards 12 that are commonly utilized within the burn-inindustry. The burn-in board 12 includes one or more sockets 14 arrangedin a desired pattern as shown in FIG. 9 of the drawings. Each of thesockets 14 removably receives, through an opening, an electronic device18 to be tested during the burn-in phase. The fluid is sprayed from thespay nozzles through this opening to engage a surface of the electronicdevice 18 contained within the sockets 14 for maintaining the desiredtemperature of the electronic devices 18 within.

The sockets 14 are electrically connectable to the electronic device 18inserted within the respective sockets 14. The burn-in board 12 is thenelectrically coupled to a control unit 60 via a communications port orother structure attached to the burn-in board 12 that controls the testsignals sent to each of the electronic devices 18 during the burn-intesting procedure. U.S. Pat. Nos. 6,404,219, 6,181,146 and 5,825,171illustrate exemplary burn-in devices and burn-in systems which aresuitable for usage with the present invention. It can be appreciatedthat various other burn-in board 12 structures and configurations may beutilized with the present invention.

In addition, a temperature sensor 62 may be attached to each of thesockets 14, directly upon the electronic devices 18 for measuring thetemperature of the electronic devices 18 during testing, or may comeembedded directly within the chips. Devices for measuring thetemperature of electronic devices 18 are commonly utilized within theburn-in industry that may be utilized with the present invention.Examples of suitable temperature sensors 62 include but are not limitedto thermocouple, thermopile, electronic devices capable of inferringtemperature of the electronic device 18 from the electronic device'spower draw, or infrared devices.

D. Spray Assembly

The spray assembly 30 has a housing containing of one or more sprayunits 40 as illustrated in FIGS. 7 and 8 of the drawings. The sprayassembly 30 preferably is comprised of a relatively flat structure,however various other structures may be utilized to construct the sprayassembly 30.

Each of the spray units 40 is arranged upon the spray assembly 30corresponding to a specific socket 14 within the burn-in board 12. Theremay or may not be a pattern for the plurality of spray units 40 such asbut not limited to a row pattern as illustrated in FIGS. 6 and 7, or astaggered pattern.

Each of the spray units 40 includes a housing structure 42 having aninterior housing cavity 43 covered by a rear plate 44 as shown in FIGS.10 through 17 of the drawings. The rear plate 44 may be attached to thehousing structure 42 using various fastening devices. The housingstructure 42 may have various sizes and shapes other than illustrated inthe drawings. A first port 45 and a second port 46 are fluidly connectedwithin the housing structure 42 which fluidly correspond to the firstportion 50 and the second portion 54 of the spray units 40 respectively.

As shown in FIGS. 10 through 17 of the drawings and for the presentembodiment of the invention, each of the spray units 40 has a firstportion 50 and a second portion 54 movably positioned within the firstportion 50, though a simpler non-movable nozzle structure may also beutilized with the present invention. FIGS. 10 and 11 illustrate theusage of a circular structure with a partially enclosed upper end.However, the first portion 50 may have various shapes and structures fordispensing the fluid onto the electronic device 18.

The first portion 50 entirely or partially surrounds the second portion54 as best illustrated in FIG. 10 of the drawings. One or more firstorifices 52 extend within the first portion 50 in various patterns. Thefirst orifices 52 may have various characteristics, shapes, sizes,styles, designs, arrangements and densities. The first orifices 52 maybe arranged to provide various spray patterns amongst multiple orifices,or various cone angles from each individual orifice, upon the electronicdevice 18. Cone angles may be of the full cone variety as is known inthe art, or of the hollow cone variety as is also known in the art, andmay vary from 10° to 60°, but are not limited to varieties, or thisangular range. It is desirable to utilize first orifices 52 that providean adjustable spray pattern depending upon the heat flux of theelectronic device 18 being tested. The first orifices 52 dispense thepressurized fluid from within the housing cavity 43 as shown in FIG. 16of the drawings.

As shown in FIG. 11 of the drawings, a main opening 48 extends into thefirst portion 50. The main opening 48 has a shape and size similar tothe second portion 54 such as but not limited to circular, square, oval,rectangular and the like. The main opening 48 is sufficient in size toallow for the sliding movement of the second portion 54 within the mainopening 48.

As shown in FIGS. 14, 16 and 17 of the drawings, a tubular portion 53extends downwardly from an interior surface of the upper end of thefirst portion 50. The tubular portion 53 preferably surrounds the mainopening 48 within the first portion 50 and extends downwardly a finitedistance for slidably receiving the second portion 54. A channel 55fluidly extends from the second port 46 to the tubular portion 53 in asealed manner to provide pressurized fluid to the second portion 54independently of the first portion 50 as best illustrated in FIG. 13 ofthe drawings. It can be appreciated that a single channel may feed boththe first portion 50 and the second portion 54.

As shown in FIG. 11 of the drawings, the second portion 54 is comprisedof a tubular structure with one or more second orifices 56 within theupper end thereof. The second orifices 56 may have variouscharacteristics, shapes, sizes, styles, designs, arrangements, patternsand densities. The second portion 54 is formed to slidably extend withinthe main opening 48 and the tubular portion 53 as best illustrated inFIGS. 16 and 17 of the drawings. At least one seal member 58 ispositioned within the second portion 54 for sealing the second portion54 within the tubular portion 53 as best illustrated in FIG. 11 of thedrawings. A longitudinal cutout 51 preferably extends into the lower endof the first portion 50 which movably fits about the channel 55 therebyallowing entry of the fluid from the channel 55 into the second portion54.

For a given cone type (full cone or hollow), each of the first orifices52 and second orifices 56 may have static spray cone angles or dynamicspray cone angles. Dynamic spray cone angles may be utilized dependentupon changing thermal management requirements for the electronic device18. For example, if it is desirable to reduce the cooling of theelectronic device 18, one or more of the orifices 52, 56 may be adjustedto reduce the surface area that is sprayed with the fluid by adjustingthe spray cone angles in response to temperature feedback. Conversely,if it is desirable to increase the cooling of the electronic device 18,one or more of the orifices 52, 56 may be adjusted to increase thesurface area that is sprayed with the fluid by adjusting the spray coneangles in response to temperature feedback.

The second portion 54 is downwardly biased within the tubular portion 53by a biasing device which may be comprised of various biasing structuressuch as but not limited to springs 57. The biasing device is preferablycomprised of one or more springs 57 attached between the tubular portion53 and the second portion 54 as illustrated in FIGS. 16 and 17 of thedrawings. One or more support members 59 are attached to a lower end ofthe tubular portion 53 and within the second portion 54 wherein thesprings 57 are connected between thereof.

When the fluid pressure within the channel 55 and the second portion 54is increased sufficiently to overcome the biasing force of the springs57, the second portion 54 is then extended outwardly from the firstportion 50 as illustrated in FIG. 17 of the drawings. A lower flangedportion extending from the second portion 54 preferably engages a lipwithin the tubular portion 53 thereby preventing the second portion 54from overextending from within the first portion 50.

When the fluid pressure within the channel 55 and the second portion 54is not sufficient to overcome the biasing force of the springs 57, thesecond portion 54 is then retained downwardly within the first portion50 with the upper ends of the first portion 50 and the second portion 54substantially level to one another as illustrated in FIG. 16 of thedrawings. It can be appreciated that varying fluid pressure within thechannel 55 and the second portion 54 will extend the second portion 54at varying distances.

The spray assembly 30 preferably includes a first inlet port 34 that isfluidly connected to the first portion 50 of the spray units 40 and asecond inlet port 36 that is fluidly connected to the second portion 54of the spray units 40. A first valve 84 preferably controls the fluidflow from the inlet tube 24 to the first inlet port 34. The first port45 within the spray units 40 receives the fluid flow from the firstinlet port 34 thereby providing the pressurized fluid to the housingcavity 43 of the spray units 40 for dispensing from the first portion 50of the spray units 40.

A second valve 86 preferably controls the fluid flow from the inlet tube24 to the second inlet port 36. The second port 46 within the sprayunits 40 receives the fluid flow from the second inlet port 36 fordispensing through the second orifices 56 within the second portion 54.

E. Dynamic Spray Control

FIG. 18 of the drawings illustrates an exemplary dynamic spray controlfor the spray units 40. The dynamic spray control may be used for one ormore of the orifices 52, 56. As shown in FIG. 18, a chamber 31 isprovided that is fluidly connected to the first orifice 52. One or morefeed ports 32 are fluidly connected to the chamber 31 for providing across fluid flow into the chamber 31 with respect to the direction ofspray from the first orifice 52. A center jet 35 extends within an inletplate 33 partially surrounding the chamber 31 opposite of the firstorifice 52. The inlet plate 33 may have various thickness, however it ispreferably to maintain the thickness of the inlet plate 33 between0.005–0.20 inches. A thicker inlet place 33 provides increased controlover the fluid flow.

A plunger 37 is positioned within the center jet 35 that has a taperedend portion as illustrated in FIG. 18 of the drawings. The plunger 37controls the amount of fluid that flows through the center jet 35. Asthe fluid flows into the chamber from the center jet 35, the fluid iscombined with fluid flowing into the chamber transversely from one ormore feed ports 32 creating a swirling effect within the chamber 31. Asthe plunger 37 is retracted from the center jet 35, an increased flowrate of the fluid is provided to the chamber 31 thereby reducing theamount of swirling of the fluid within the chamber 31 that occursbecause of the feed port 32. The center jet 35 and the plunger 37 may besized such that when the plunger 37 is fully retracted from the centerjet 35, a relatively straight jet of fluid passes through the firstorifice 52 instead of an atomized spray.

Various technologies may be utilized to control the position of theplunger 37 within the center jet 35 such as but not limited to digitalstepper motors, linear actuators, magnetostrictive actuators ormechanical devices. In addition, each plunger 37 may be controlledindividually or in a group by using a common mechanical or electricalstructure by the control unit 60. The plunger 37 may be positionedwithin the feed port 32. In addition, the inlet plate 33 may be movedwith respect to the plunger 37 in a stationary position to create asimilar effect. A piezo-crystal or magnetostrictive material positionedbetween the inlet plate 33 and the walls of the chamber 31 may beutilized to manipulate the position of the inlet plate 33. Various otherdevices may be utilized to control the flow of fluid into the chamber 31and thereby control the characteristics of the fluid spray dispersedfrom the first orifice 52.

F. Fluid Distribution System

The reservoir 80 is comprised of a container structure capable ofretaining a desired volume of fluid. The reservoir 80 may have variousshapes, sizes and structures which are commonly utilized to construct areservoir 80. The fluid utilized within the present invention ispreferably comprised of a dielectric fluid such as but not limited tohydrofluoroether (HFE). However, the fluid utilized may be comprised ofa non-dielectric such as but not limited to water.

The reservoir 80 may include a thermal conditioning unit 90 forincreasing or decreasing the temperature of the fluid within thereservoir 80 to a desired temperature to be sprayed upon the electronicdevices 18 during the burn-in process. The thermal conditioning unit 90may be comprised of a combination heater unit and cooling unit. A heatexchanger may be utilized to increase the temperature of the fluidwithin the reservoir 80 by exchanging the heat from the fluid returningfrom the spray enclosure 20 after spraying upon the electronic devices18. An inline heater/cooler may also be utilized to thermally conditionthe fluid prior to or after spraying from the nozzles.

A main pump 82 is fluidly connected to the reservoir 80 for drawing thedielectric fluid from within the reservoir 80. The fluid pressure withinthe fluid distribution system may be maintained by operation of the mainpump 82 and/or a return valve 85 which allows for the return of fluid tothe reservoir 80 to lower the fluid pressure as shown in FIG. 1 of thedrawings. Various other pressure regulating devices may be utilized tocontrol the fluid pressure on the pressurized side of the pump. The mainpump 82 is fluidly connected to the first valve 84 and the second valve86 as further illustrated in FIG. 1 of the drawings thereby providingpressurized fluid to the spray units 40 at the desired pressure.

As shown in FIG. 1 of the drawings, a fluid collector 28 is positionedwithin the spray enclosure 20 for collecting the fluid after beingsprayed upon the electronic devices 18. The fluid collector 28 may becomprised of various collecting devices such as but not limited to a panstructure. The fluid collector 28 is fluidly connected to the reservoir80 for returning the used fluid to the reservoir 80. A filter device maybe positioned within the fluid collector 28 or the reservoir 80 forfiltering the fluid after being sprayed upon the electronic devices 18for removing undesirable particulate materials and chemicals which mightinterfere with the operation of the spray units 40.

A vapor recovery unit 70 may be fluidly connected to or within the sprayenclosure 20 for collecting and condensing fluid that has undergone aphase change to vapor. The vapor recovery unit 70 may be comprised ofcondensing coils and similar other devices capable of condensing vapor.The vapor recovery unit 70 may be utilized during and after the burn-inprocess.

G. Control Unit

The control unit 60 may be comprised of various electronic devicescapable of communicating with and controlling the burn-in board 12, thethermal conditioning unit 90, the main pump 82, the first valve 84, thesecond valve 86, the return valve 85 and the vapor recovery unit 70. Thecontrol unit 60 may be comprised of a computer or other electronicdevice capable of receiving and storing commands.

The control unit 60 may communicate with the external electrical devicessuch as but not limited to electrically or via communications signal.The control unit 60 may be programmed to operate the external devices atvarious operating levels such as but not limited to controlling thetemperature of the fluid within the reservoir 80, controlling the fluidpressure and flow rate emitted by the main pump 82, controlling thespray pattern and flow of the orifices 52, 56, and controlling the flowof fluid to the spray unit 40. It can be appreciated that more than onecontrol unit 60 may be utilized to control one or more of the componentsof the present invention.

H. Operation

In use, the electronic devices 18 are properly positioned within thesockets 14 of the burn-board 12. The burn-in board 12 is then positionedwithin the spray enclosure 20 with the surface of the electronic devices18 facing substantially downwardly toward the upper end of thecorresponding spray units 40. The dielectric fluid within the reservoir80 is heated to a desired temperature for cooling or heating theelectronic devices 18 with or without using a conditioning unit 90. Themain pump 82 and valves 84, 86 may be utilized to achieve and maintainthe target junction temperature even though the fluid temperature maynot be the desired temperature. The main pump 82 is operated to providethe pressurized fluid to the spray assembly 30.

If the electronic devices 18 being burned in have a relatively highprofile (e.g. electronic devices 18 with integrated heat sinks whichhave a lower heat flux thereby requiring less fluid flow for coolingpurposes), then both the first valve 84 and the second valve 86 areopened to provide fluid to the first portion 50 and the second portion54 at a substantially constant pressure. As further shown in FIG. 16 ofthe drawings, fluid is sprayed from both the first orifices 52 and thesecond orifices 56 without the second portion 54 elevated with respectto the first portion 50.

If the electronic devices 18 being burned-in have a low profile withinthe socket as illustrated in FIG. 17 of the drawings (e.g. electronicdevices 18 without integrated heat sinks which have a higher heat fluxthereby requiring increased fluid flow for cooling purposes), then thefirst valve 84 is closed and the second valve 86 is opened withincreased fluid pressure being supplied to the second portion 54 therebyextending the second portion 54 upwardly from the first portion 50 nearthe electronic device 18.

It is desirable to decrease the spraying distance between the distal endof the second portion 54 and the surface of the electronic device 18when high heat flux conditions exist requiring additional cooling.Conversely, it is desirable to increase the spraying distance betweenthe distal end of the second portion 54 and the surface of theelectronic device 18 when low heat flux conditions exist requiring lesscooling.

As the fluid or fluid is sprayed upon the electronic device 18, thecontrol unit 60 applies the desired voltage to the electronic devices 18for burn-in testing purposes thereby increasing or lowering thetemperature of the electronic device 18. If the device temperature ofthe electronic device 18 rises above a desired temperature (e.g. 100°Celsius), then the flow rate X of the fluid is increased to the sprayunits 40 as shown in FIG. 3 of the drawings. In addition to orindependent of increasing the flow rate X, the spray pattern sizeemitted from one or more of the orifices 52, 56 may be increased toengage an increased surface of the electronic device 18 of theelectronic device thereby increasing the cooling of the electronicdevice 18. Instead of increasing the size of the spray pattern forincreasing the cooling of the electronic device, the spray pattern mayalso be directed to and focused upon a specific area of the electronicdevice 18 that has a high heat flux compared to other areas of theelectronic device 18.

If the device temperature of the electronic device 18 is lowered below adesired temperature, then the flow rate X of the fluid is decreased tothe spray units 40 as shown in FIG. 3 of the drawings. In addition to orindependent of decreasing the flow rate X, the spray pattern sizeemitted from one or more of the orifices 52, 56 may be decreased toengage an reduced surface of the electronic device 18 thereby reducingthe cooling of the electronic device 18. Instead of decreasing the sizeof the spray pattern for decreasing the cooling of the electronicdevice, the spray pattern may also be directed away from a specific areaof the electronic device 18 that has a high heat flux compared to otherareas of the electronic device 18. In addition, the spray pattern may beincreased in size thereby reducing the spray engaging high heat fluxareas of the electronic device 18.

If the device temperature of the electronic device 18 is approximatelyequal to a desired temperature, then the flow rate X of the fluid ismaintained to the spray units 40 as shown in FIG. 3 of the drawings. Inaddition, the spray pattern size is preferably maintained relativelyconstant for each of the orifices 52, 56 where the device temperature ofthe electronic device 18 is approximately equal to the desiredtemperature.

In order to control the device temperature of the electronic device 18,the power level may also be increased or lowered independently or inconjunction with the control of the fluid flow rate. The AC and DC powerlevels may be adjusted to manipulate the electronic device'stemperature.

Various methods of thermal management may be employed for the electronicdevices 18. For adequately low heat fluxes, it may be appropriate tocool the electronic devices 18 through purely forced convection (i.e. noeffective evaporation of the coolant occurs). For intermediate heatfluxes, it may be appropriate to utilize a combination of forcedconvection and phase change heat transfer (i.e. the latter methodresulting in evaporation of the coolant). For the highest level of heatfluxes, it may be appropriate to optimize purely on phase change heattransfer. For optimization on an approach that is dominated by phasechange, it is critical to have a system design and method of operationthat allows the maintenance of a thin coolant film on the electronicdevices at all times. Upon coolant delivery to the electronic devices18, all coolant is returned to the reservoir 80 for reuse. In situationswhere vapor is generated, the system is designed such that the pressuregenerated by the vapor assists in the return of the vapor and anycondensed or unevaporated coolant back to the reservoir 80.

As the fluid is sprayed upon the electronic devices 18, the fluidengaging the electronic devices 18 may be partially vaporized. The vaporis eventually condensed as the temperature of the vapor is reduced aftershutdown. The vapor may also be condensed by pressure increases withinthe spray enclosure 20 or via the vapor recovery unit 70 during or afteroperation of the present invention. The non-vaporized fluid passesdownwardly within the spray enclosure 20 to the fluid collector 28 wherethe fluid is then filtered and returned to the reservoir 80 for reuse.

This process continues until the electronic devices 18 are fullyburned-in over the required amount of time. Once the burn-in process iscompleted, the flow of the fluid is terminated. All vapor is recoveredduring the fluid recovery phase, and unevaporated coolant on the burn-inboard 12, sockets and other, is made to evaporate for subsequentrecovery. The burn-in board 12 and electronic devices 18 are thenremoved from the spray enclosure 20 for replacement with other burn-inboards 12 and electronic devices 18.

What has been described and illustrated herein is a preferred embodimentof the invention along with some of its variations. The terms,descriptions and figures used herein are set forth by way ofillustration only and are not meant as limitations. Those skilled in theart will recognize that many variations are possible within the spiritand scope of the invention, which is intended to be defined by thefollowing claims (and their equivalents) in which all terms are meant intheir broadest reasonable sense unless otherwise indicated. Any headingsutilized within the description are for convenience only and have nolegal or limiting effect.

1. A method of operating a thermal management system for thermallymanaging at least one electronic device, said method comprising thesteps of: providing at least one spray unit and at least one electronicdevice in opposition to said at least one spray unit; spraying a fluidfrom said at least one spray unit towards said at least one electronicdevice, wherein said dispensed fluid has a spray cone angle; andadjusting said spray cone angle to control a device temperature of saidat least one electronic device.
 2. The method of operating a thermalmanagement system of claim 1, including the step of increasingelectrical power to said at least one electronic device if a devicetemperature of said at least one electronic device is below a desiredtemperature and decreasing electrical power to said at least oneelectronic device if a device temperature of said at least oneelectronic device is above a desired temperature.
 3. The method ofoperating a thermal management system of claim 1, wherein said fluid iscomprised of a dielectric fluid.
 4. The method of operating a thermalmanagement system of claim 1, wherein said fluid is comprised of anon-dielectric fluid.
 5. A method of operating a thermal managementsystem for thermally managing at least one electronic device, saidmethod comprising the steps of: spraying a fluid from at least one sprayunit towards at least one electronic device, wherein said dispensedfluid has a spray cone angle; and adjusting said spray cone angle tocontrol a device temperature of said at least one electronic device. 6.The method of operating a thermal management system of claim 5,including the step of increasing electrical power to said at least oneelectronic device if a device temperature of said at least oneelectronic device is below a desired temperature and decreasingelectrical power to said at least one electronic device if a devicetemperature of said at least one electronic device is above a desiredtemperature.
 7. The method of operating a thermal management system ofclaim 5, wherein said fluid is comprised of a dielectric fluid.
 8. Themethod of operating a thermal management system of claim 5, wherein saidfluid is comprised of a non-dielectric fluid.
 9. A method of operating athermal management system for thermally managing at least one electronicdevice, said method comprising the steps of: spraying a continuous andnon-incremental spray of liquid coolant from at least one atomizer of aspray unit towards at least one electronic device, wherein saidcontinuous and non-incremental spray of liquid coolant has a spraycharacteristic; determining a temperature of said at least oneelectronic device; and adjusting said spray characteristic in responseto said temperature to control said temperature of said at least oneelectronic device.
 10. The method of operating a thermal managementsystem of claim 9, including the step of increasing electrical power tosaid at least one electronic device if said temperature of said at leastone electronic device is below a desired temperature and decreasingelectrical power to said at least one electronic device if saidtemperature of said at least one electronic device is above a desiredtemperature.
 11. The method of operating a thermal management system ofclaim 9, wherein said fluid is comprised of a dielectric fluid.
 12. Themethod of operating a thermal management system of claim 9, wherein saidfluid is comprised of a non-dielectric fluid.